I would not worry too much about pines(pinacea family) rotting faster..this statement is simply not true. take cedar for instance..in the cypress genus. these trees well know for their resistance to breakdown when submerged. other 'pines' also fit the bill.
the only ting I would suggest is you try to get wood that has been submerged as the water will allow the resins to slowly release.
what you may find out about many deciduous trees is they they may actually break down more quickly.
I will surely consider using them.